Preparation Of Hydrophobic Zeolite 13X And Its Application In H₂O/CO₂ Adsorption

Global warming caused by greenhouse gases has been an urgent environmental issue in 21th century.Carbon dioxide(CO2)discharged by industry is regarded as the main contributor of greenhouse gases.Therefore,reducing the discharge of CO2,fixing or recycling CO2 is the primary method to remit climate warning.Adsorption and separation is the most frequently employed technique to fix CO2,in which solid absorbents are used and exhibited priority on improving absorption property.Zeolite 13X with uniform micro-pores can adsorb gases selectively according to the sizes and shapes of gas molecules,serving as a potential material for the adsorption and separation of CO2.However,improving the hydrophobicity of zeolite 13X is essential because the adsorption of CO2 is interfered seriously by water vapor in the real waste gases discharged by industries.Therefore,it is essential to modify 13X zeolite to improve the hydrophobicity,which will facilitate the separation of CO2 and H2O.In the present study,we investigate the preparation of hydrophobic core/shell zeolite 13X@SiO2 and thin membrane Si-13X zeolite,in addition to the absorption property of zeolite 13X before/after modification.For the preparation of core/shell zeolite,ethanol template and aqueous template method are employed.The characterization results indicate that the 13X@SiO2 prepared from ethanol template method has compact and uniform SiO2 shell.The thickness and the crystal structure keeps constant after modification with octadecyltrichlorosilane(OTS).The hydrophobicity is enhanced significantly.At the same time,Si-13X zeolite prepared by using SiCl4 deposition method does not behave nonuniform membrane.The improvement on hydrophobicity is not as good as core/shell 13X@SiO2,which is demonstrated by the adsorption experiments on water.Zeolite 13X exhibits strong adsorption ability on water and its adsorption amount increases from 8.7 mmol/g to 14.1 mmol/g with the humanity increase from 6.2%to 19.4%.Meanwhile,the mass transfer zone gets shorter and adsorption rate is enhanced with the humanity increase.When humanity is 40%,the adsorption capacities on H2O and CO2 are 15.03 mmol/g and 0.39 mmol/g,respectively.The binary component H2O and CO2 adsorption results indicate that with the increase of humanity,the adsorption on H2O increases and the the adsorption on CO2 decreases.With modification using OTS,the 13X@SiO2-OTS-2.0 provides lower adsorption capacity of 8.38 mmol/g on water at 50 ?.While the adsorption capacity for zeolite 13X is 13.92 mmol/g on water at the identical conditions.The thermal analysis results indicate that the adsorption capacities on CO2 are 3.63 mmol/g and 2.73 mmol/g for zeolite 13X and 13X@SiO2-OTS-2.0,respectively.In addition,the modification with OTS give rise to the decrease of water adsorption capacity in binary component gases adsorption test,which is demonstrated by the decrease of 5.71 mmol/g and 0.62 mmol/g on H2O and CO2 adsorption capacities.The results indicate that this hydrophobic modification scheme significantly reduces the adsorption on H2O while the adsorption capacity on CO2 is reduced slightly,demonstrating the potential application of 13X@SiO2-OTS as solid adsorbents for the separation of CO2 in humid waste gases.Liquid deposition modified zeolite,Si-13X shows adsorption capacity of 2.29 mmol/g at 60 ?.Compared with zeolite,the adsorption capacity significantly declines by 36.9%.While the water adsorption results illustrate the figure declines from 13.92 mmol/g to 9.84mmol/g with a 29.3%decline.In addition,the adsorption results on binary components mixed gas of CO2 and H2O illustrate that the adsorption capacities on H2O and CO2 drop by 17%and 40%,respectively.It is concluded from the above results that hydrophobic core/shell 13X@SiO2-OTS show excellent hydrophobic ity and superiority in separation of H2O and CO2 over thin membrane Si-13X,which could be employed as the hydrophobic zeolite absorbent for the adsorption of CO2 in industry.